Magnetic chuck



May 17, 1960 H. ARTER ETAL MAGNETIC CHUCK 2 Sheets-Sheet 2 OriginalFiled Nov. 15, 1952 IA VE TORS MW M3784 47' roR/yEy Mfr/4m? UnitedStates Patent MAGNETIC CHUCK Harry Arter, Worcester, and Arlon G.Sangster, Leominster, Mass., assignors, by mesne assignments, toSundstrand Corporation, a corporation of Illinois 4 Claims. (Cl.29-155-59) This application is a division of our prior applicationSerial No. 320,795, filed November 15, 1952, now abandoned, and relatesto new and improved magnetic chucks and similar holding devices, and theprincipal object of the present invention resides in the provision of anew and improved chuck design that is greatly simplified over the priorart while retaining and enhancing the holding power of the chuck, thenovel magnetic chuck of the present invention being much thinner or lessin height, cheaper and faster to manufacture, lighter in weight, andstill retaining the qualities of prior art chucks.

Another object of the invention resides in the provision of atop platefor a magnetic chuck comprising a single piece of magnetic materialprovided with a series of relatively narrow slots cut therein andarranged substantially concentrically but with gaps to provide forradial solid portions that are not cut to retain the rigidity andstrength of the metal, said gaps being filled with nonmagnetic materialand providing a series of narrow gaps alternating with wider magneticflux-carrying portions, said top plate being such as to be directlyplaced on the box of the chuck containing the coils or magnets providingthe flux, thus completely doing away with the prior art spreader platenormally required in order to properly distribute the magnetic lines offorce, but obviated in the present case due to the construction of thetop plate and due to the combination of the top plate and the coil boxconstruction.

Another object of the invention resides in the provision of a novelmethod of making the top plate in pairs by flame cutting a series ofgenerally concentric narrow slots in a pair of plates, welding the twoplates together at the edges thereof, applying non-magnetic weldingmaterial to the then exposed edges of the slots so as to form trenchesor recesses that may be easily and quickly filled with non-magneticmaterial, separating the plates by removing the circumferential weld,and then filling the trenches or recesses with non-magnetic material toform the non-magnetic gaps or barriers.

Other objects and advantages of the invention will appear hereinafter.

Reference is to be had to the accompanying drawings, in which:

Fig. 1 is a view in side elevation showing the exterior appearance ofthe new chuck, parts of the machine to which it is applied being shownin section;

Fig. 2 is a diametrical section through the chuck;

Fig. 3 is a plan view of the top plate;

Fig. 4 illustrates a step in the method of making the same;

Fig. 5 is a view similar to Fig. 4 but having parts in section; and

Fig. 6 illustrates the parts of Fig. 5 separated and ready for the finalstep of filling the trenches or recesses of the top plate withnon-magnetic material.

To illustrate the present case, the novel chuck is elected to be shownas being of circular form adapted to be secured to the rotating bed 10of a machine tool such as a surface grinder, the bed being rotated by aworm or the like 12 mounted in the body of the machine 14. The chuckitself is generally indicated at 16 and comprises a top plate 1 8 and abox 20, the latter containing the magnetic flux producing coils ormagnets. Whereas the invention is thus disclosed in a practical form asbeing applied to a rotary chuck, the invention is not necessarilylimited to such a rotary chuck.

Construction of the new chuck is extremely simple and is shown insection in Fig. 2 as comprising the top plate '18 bolted to the box 20,as for instance by through bolts 22, that may also take into therotating table 10 as indicated by the exposed threaded ends of the boltsat 24, and bolts 25 that extend from the box into the plate. Also asshown, the box 20 comprises a series of annular grooves 26, 28, 30, thatare open at their tops and closed by the top plate, as is clearlyapparent. The grooves are separated by upstanding rings or lands 32,accommodating bolts 25. The rings 32 are arranged concentrically and atdistances from the center 34 such as to provide for an even fluxdistribution in the top plate, it being recognized that the coils to beheld in the grooves in-' crease in diameter from groove '30 radiallyoutwardly. It is to be observed that the number of coils and spacingthereof may be varied to suit the size of the chuck, but it is alsodesirable to so space the annular coils as to provide uniform fluxdistribution over the gaps in the top plate.

The top plate itself is shown as comprising a single solid metal disc ofappropriate thickness. The pole pattern is shown best in Fig. 3 and thechuck is simply a single solid piece of magnetic material provided witha series of concentric gaps arranged with regard to the coils in thebox, so as to provide a uniform flux distribution throughout the entiretop plate. The gaps are in the form of interrupted circles, so that theradial portions of the top plate indicated at '36 provide physicalstrength without loss of fiux density and it will be apparent that verysmall workpieces may be held to the top plate illustrated.

The solid magnetic plate is flame cut from top to bottom on the arcsshown in Fig. 3. It is necessary of course to fill the flame cut slotswith non-magnetic material as by pouring the material in a fluid stateand allowing it to harden. in order to do this it is necessary toprovide a darn or barrier at the bottom of each slot 38, and this isdone by applying small amounts of welding material of non-magneticnature at one side surface of the plate as best indicated in Figs. 5 and6 at 40. However, if this is done to the plate in a free state, the samebecomes warped due to the shrinking of the slots at one side thereofwhen the metal cools, and therefore this invention proposes to take twoflame cut discs 18 and weld them together at the circumferential edgesthereof as at 42. Then one weld 40 is provided to close a slot 44 at oneside surface of the two combined plates and the corresponding weldingbarrier is provided at the opposite side surface thereof. The next weld40 is made at the first side, and the fourth at the opposite side, etc.and thus the dams are provided alternately on the side surfaces of thetwo welded plates across the entire areas of the plates.

The side surfaces being thus processed alternately, the combined discsare annealed, and then the welding 42 is machined off. When separated,the discs are just as flat as originally made, and the slots may then befilled with the non-magnetic material in the usual way.

This process of making the top plate provides a practical means forachieving the desired result which is not otherwise obtainable sinceonce one of the plates is warped, it is practically impossible toreplace it in original flat state. These plates with the welds 40 cannotbe heated and flattened, as this would weaken or even destroy 3 thesewelds, as well as impairing the magnetic qualifies of the plate itself.

As soon as the plates have been separated as in Fig. 6, the remainingrecesses or trenches '44 produced by the welds 40 are filled withnon-magnetic material and the top plate is completely finished exceptfor polishing operations.

It will be seen that this invention provides an extremely simple andinexpensive magnetic chuck which may be produced faster and in greaterquantity than those of the prior art; the new chuck does away withso-called spreader plates formerly thought to be necessary anddesirable, provides an extremely practical and efiicient pole patternfor holding pieces of either small or large size or a thick or thinsection, and greatly reduces the height or thickness of the chuck.

Having thus described our invention and the advantages thereof, we donot wish to be limited to the details herein disclosed, otherwise thanas set forth in the claims, but what we claim is:

1. The method of making top plates for magnetic holddevices comprisingthe steps of providing a pair of similar slotted magnetic members havinggenerally flat parallel surfaces, securing the slotted member togetherin superimposed fiat-wise condition against warping during welding,forming non-magnetic welds closing the slots in each member at onesurface only of each member while the plates are so secured, and thenseparating the members after cooling.

2. The method of making top plates for magnetic holding devicescomprising flame cutting a series of spaced coextensive slots through apair of flat solid magnetic members, securing the slotted memberstogether flatly by welding at the edges thereof, blocking each exposedslot edge alternately in the plates by welding the edges of a slot inone plate, then similarly welding the corresponding slot in the otherplate until all slots are blocked, separating the members after cooling,and filling the closed slots with non-magnetic material.

3. The method of making top plates for magnetic holding devicescomprising the steps of providing a pair of magnetic plates with throughgaps therein, securing said plates flatwise together in generallycoextensive superposed relation by welding at the plate edges, blockingthe exposed edges of the gaps in both plates by non-magnetic welding atsaid gap edges, separating the plates after cooling, and filling theexposed, blocked gaps with non-magnetic material.

4. The method of making top plates for magnetic holding devicescomprising the steps of providing a pair of magnetic plates with throughgaps therein, said plates being substantially identical in compositionand structure, securing said plates together in generally coextensivesuperposed relation by circumferentially' welding said plates at themeeting edges thereof, blocking the exposed edges of the gaps in bothplates by alternate non-magnetic welding at said gap edges at oppositeside surfaces of the combined plates and with the same number and typeof welds in each plate, separating the plates after cooling, and fillingthe exposed, blocked gaps with non-magnetic material.

References Cited in the file of this patent UNITED STATES PATENTS1,232,512 Dowues et al. July 10, 1917 2,388,737 Gotha Nov. 13, 19452,465,251 Meier Mar. 22, 1949

